Summaries of newsworthy papers include Ecology: The unrealized power of parasites, Materials: Flexible electronic networks of carbon nanotubes and Astrophysics: Accretion disks show their true colours

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VOL.454 NO.7203 DATED 24 JULY 2008

This press release contains:

· Summaries of newsworthy papers:

Ecology: The unrealized power of parasites

Hydrogeology: Understanding arsenic cycles

News and Opinion: China’s Challenges

Materials: Flexible electronic networks of carbon nanotubes

Astrophysics: Accretion disks show their true colours

· Mention of papers to be published at the same time with the same embargo

· Geographical listing of authors

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[1] Ecology: The unrealized power of parasites (pp515-518)

Parasitic organisms may have more of an influence on ecosystems than we previously thought, according to an ecological survey of river estuaries in California and Mexico. Parasites have often been dismissed as negligible contributors to the overall biomass of ecosystems, but in this new survey their biomass was found to exceed that of the ecosystem's top predators.

Researchers led by Armand Kuris surveyed hundreds of species living on three river estuaries — one in California and two in Mexico's Baja California — including 138 species of infectious parasite. As they report in this week's Nature, parasites represented as much as 3% of the overall biomass of the ecosystem in some areas.

Although these results only deal with one type of ecosystem, that figure is an order of magnitude higher than previous estimates of parasite biomass in other ecosystems, such as coral reefs, the authors point out. By far the most abundant parasite in the river estuaries was a trematode species that infects and castrates snails, effectively turning the snail into a production line for more parasites. The survey shows that, in some estuaries, the snail biomass controlled by these parasites was greater than that of free-living snails.

A clear demonstration of how a groundwater flow system can control arsenic levels in southeast Asia is presented in Nature this week. A detailed study of the upper Mekong delta of Cambodia reveals the source of arsenic-contaminated ground water, and provides a potential framework for predicting future groundwater quality in the region.

Tens of millions of people in Asia routinely consume water that has dangerously high arsenic levels. Arsenic is naturally derived from eroded Himalayan sediments, but the processes controlling the aqueous concentrations and the location of arsenic release to pore water remain unclear.

Scott Fendorf and colleagues use hydrologic and biogeochemical measurements to build a model of arsenic release and transport through the Mekong delta. They show that arsenic is released from near-surface wetland sediments and transported through underlying aquifers back to the river. This natural cycle has been occurring for millennia but can be influenced by land use changes such as irrigation pumping, agricultural intensification and urbanization.

The results represent a model for understanding pre-disturbance conditions for other major deltas in Asia and indicate that release and transport of arsenic are sensitive to ongoing and impending anthropogenic disturbances.

A special issue of Nature this week explores the challenges that China faces en route to becoming a major scientific player, and those that its rapid development poses to the rest of the world. A statistical round-up captures just what a research colossus the country has become over the past few years, with its mushrooming publications, graduates and funding. Three News Features catch up with space, energy, health and the environment in China, focusing in on clean coal technology and the potentially devastating effects caused by the melting of the Tibetan glaciers.

A Commentary explores the tensions arising from China’s ambition to become a global science player while still needing to meet urgent needs in internal applied research. Meanwhile a suite of ‘vox profs’ from Chinese scientists who have stayed in the country, left or returned, give some ground truth on topics from gender equality in the lab to the difficulties of team building with postdocs from the headstrong ‘little king’ generation. Finally, two pieces probe the origins and alarming social legacy of the ‘one-child’ policy.

Lightweight, flexible and shock resistant — in terms of their mechanical properties, integrated circuits formed on sheets of plastic outclass those formed on rigid substrates such as semiconductor wafers or glass. A paper in this week’s Nature reports improvements in the electrical performance of integrated circuits through the engineering of webs of carbon nanotubes onto bendable plastics.

John Rogers and his colleagues have created small- to medium-scale integrated digital circuits with around 100 transistors by using random networks of single-walled carbon nanotubes on plastic substrates. Their devices show excellent electronic properties, with superior subthreshold characteristics, operating voltages, power consumption and switching speeds.

The authors expect that their approach will expand the range of potential applications as well as reducing their cost. Possibilities unattainable with conventional wafer-based electronics could include paper-like displays, wearable personal health-monitoring devices and intelligent food packages, for example.

Quasars are the brilliant cores of remote galaxies, at the hearts of which lie supermassive black holes that can generate enough power to outshine the Sun a trillion times. These mighty power sources are fuelled by interstellar gas, thought to be sucked into the hole from a surrounding ‘accretion disk’. A paper in this week’s Nature verifies a long-standing prediction about the intensely luminous radiation emitted by these accretion disks.

Models of the disks cannot quite be reconciled with some of the observations — in particular, the radiation spectrum emitted at long wavelengths appears not to be as blue as it should be. Makoto Kishimoto and colleagues investigated this discrepancy by studying the polarized light from six quasars. This enabled them to subtract emission from hot dust outside the accretion disk, and thereby demonstrate that the disk spectrum is as blue as predicted.

The standard picture of the accretion disk is therefore vindicated. The authors believe that further measurements could eventually provide valuable insight into how and where the disk ends.

***These papers will be published electronically on Nature's website on 23 July at 1800 London time / 1300 US Eastern time (which is also when the embargo lifts) as part of our AOP (ahead of print) programme. Although we have included them on this release to avoid multiple mailings they will not appear in print on 24 July, but at a later date. ***

[7] Spatio-temporal correlations and visual signalling in a complete neuronal population
DOI: 10.1038/nature07140

[11] A blend of small molecules regulates both mating and development in Caenorhabditis elegans
DOI: 10.1038/nature07168

GEOGRAPHICAL LISTING OF AUTHORS…

The following list of places refers to the whereabouts of authors on the papers numbered in this release. For example, London: 4 - this means that on paper number four, there will be at least one author affiliated to an institute or company in London. The listing may be for an author's main affiliation, or for a place where they are working temporarily. Please see the PDF of the paper for full details.

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